1. Field of the Invention
The present invention relates to a valve timing regulation device for varying the opening and closing timing of one or both of an intake valve or an exhaust valve in response to the operational conditions of an internal combustion engine.
2. Description of the Prior Art
A conventional valve timing regulation device comprises a case which is mounted to rotate freely on a camshaft which opens and closes intake and exhaust valves of an internal combustion engine and which is rotated by an output force of the internal combustion engine, a rotor which is stored in the case, is engaged with the camshaft and which rotates relative to the case, an engagement hole for locking which is provided on one of the case or the rotor, and a lock pin which is provided on the other of the case or the rotor which does not mount the engagement hole, which engages by insertion into the engagement hole due to a mechanical biasing force to lock the relative rotation of the rotor and the case and which disengages from the engagement hole due to a hydraulic control force to release the locking. The case has a plurality of shoes which project inwardly and the rotor has a plurality of vanes which project outwardly. The supply of hydraulic pressure selectively to advancing and retarding hydraulic pressure chambers which are formed between the shoes and vanes is automatically controlled in response to the operational conditions of the internal combustion engine. Thus the rotor is operated in an advancing or retarding direction due to a pressure differential between the advancing and retarding hydraulic pressure chambers. The opening and closing timing of the intake and exhaust valves is controlled as a result. Each vane of the rotor and each shoe of the case has a tip seal on each respective tip to prevent the leakage of oil between the advancing and retarding hydraulic pressure chambers.
A valve timing regulation device normally entails the requirement of minimizing the clearance between the sliding faces of the case, its covering member and the rotor. The case, its covering member and the rotor expand or contract due to heat as a result of temperature variation during operation of the internal combustion engine. At such times, when the linear expansion coefficient of the case, its covering member and the rotor differs greatly, the clearance with respect to the sliding face undergoes a large variation and considerable oil leakage can be generated from the resulting clearance. Conversely the rotor in a lock release state may be pressed onto the case due to thermal expansion and stopped from rotating. This results in impairment to the control performance of the valve opening and closing timing.
It has been proposed to form the case, its covering member and the rotor from a material with the same linear expansion coefficient in order to reduce variation in the clearance due to temperature variations during operation of the internal combustion engine as much as possible.
However even in valve timing regulation devices in which the case, its covering member and the rotor are formed from different materials, it is still necessary to suppress variations in the clearance, which is set between the sliding faces of the case, its covering member and the rotor which results from temperature variations during operation of the internal combustion engine.
Since a conventional valve timing regulation device is formed as discussed above, when the rotor and the case are formed from the same material, for example from an aluminum material with the same linear expansion coefficient, a locking pin is formed in one of the rotor and the case with an engagement hole being formed in the remaining component. In this way, the engagement hole must have a maximum mechanical strength since a shear force operates in the direction of rotation of the rotor when the lock pin is engaged. However an engagement hole provided on the case or the rotor which is formed from an aluminum material does not have sufficient strength results in early wear or deformation of the engagement hole. As a result not only is shaking and normal noise generated on engagement of the lock pin and the engagement hole, there is a high probability of considerable damage to the control performance of the valve and closing timing.
A conventional valve timing regulation device entails various problems with respect to the disposition of a lock means on either the case or the rotor or the direction of operation of the lock means with respect to the rotational center of the case and the rotor even when the case, its covering member and the rotor are formed from different materials. For example, when a lock pin is formed near the case is formed from an iron material and an engagement hole is provided on the rotor and is formed from an aluminum material, as discussed above, in the same way as when the case and the rotor are formed from the same material, early wear or deformation of the engagement hole occurs due to insufficient strength of the engagement hole. Thus a deviation is generated between the lock pin and the engagement hole during locking of the rotor and there is a high probability of considerable damage to the control performance of the valve opening and closing timing.
In particular as discussed above, when the case, its covering member and the rotor are formed from different materials, even under any kind of temperature conditions during operation of the internal combustion engine, it is ideal to maintain an optimal clearance to prevent oil leakage and allow relative rotation of the sliding faces of the case and the rotor. For this reason, the case and the rotor must have set dimensions depending on the temperature conditions. However the problem has arisen that a technical solution has not been found.